The loss of harvested crops, which results from diseases of plants, represents a world-wide problem. For example, potatoes suffering from potato wet rot or potato rot (rotting of the tuber) and black leg or black stem (rotting of the lower stem sections) after infection by the phytopathogenic bacterium Erwinia carotovora, results in crop losses to an estimated amount of 100 million dollars world-wide (Perombelon et al., 1980, Ann. Rev. Phytopathol. 18: 361-387). There is a number of studies dealing with the transmission of resistance factors to plants by means of genetic engineering (Lamb et al., 1992, Bio/Technology 10: 1436-1445; Hain et al., 1994, Current Opinion in Biotechnology, 125-130; Zhu et al., 1994, Bio/Technology 12: 807-812). In order to increase the resistance of potatoes to Erwinia carotovora, the T4 lysozyme gene of the bacteriophage T4 was expressed in transgenic potatoes (During et al., 1993, Plant J. 3: 587-598).
However, since bacterial diseases of plants often spread under anaerobic conditions, the resistance factors for plants transmitted so far, are effective only in a very restricted extent. This applies particularly to the above-mentioned disease of potatoes suffering from potato rot and black leg, since the infection caused by Erwinia carotovora takes place predominantly under anaerobic conditions. This effect is increased by the formation of a mucus from bacteria and degradation products of vegetable cell membranes. Regarding an effective expression of an antibacterial protein under optimum conditions, it is desirable to control the corresponding foreign gene by a promoter active under these conditions.
Three anaerobic promoters have been tested in transgenic plants so far. These are the Adh1 promoter from corn, the Adh promoter from Arabidopsis thaliana and the GapC promoter from Arabidopsis thaliana. The Adh1 promoter from corn was investigated in tobacco and rice (Ellis et al., 1987, EMBO J. 6: 11-16; Kyozuka et al., 1991, Mol. Gen. Genet. 228: 40-48). The GapC promoter from Arabidopsis was investigated in tobacco (Yang et al., 1993, Plant Physiol. 101: 209-210), and the Adh promoter from Arabidopsis was investigated in Arabidopsis as such (Dolferus et al., 1994, Plant Physiol. 105: 1075-1087). It turned out that all promoters convey only 2 to 81 times the induction of the reporter gene over the background and are not active in all of the tissues.